The field of this invention is that of compartment heaters for automotive vehicles and the invention relates more particularly to a compartment heater system having an electrical resistance heater of positive temperature coefficient supplementing a hot-water-based heater type to more quickly improve passenger comfort after engine start-up on a cold day.
Recent trends toward automotive engines operating with greater efficiencies and lower heat rejection rates have progressively reduced the amount of "waste" heat from the engine available for use for heating the vehicle passenger compartment. At the same time there is a desire to reduce compartment heat-up time and/or to increase passenger compartment temperature. Over the past several years there has been a growing interest not only in improving the performance of currently-used hot-water-based compartment heaters but also to employ supplementary heaters, particularly for supplying heat to the passenger compartment during the engine warm-up period on a cold day when the output from the hot-water-based heater is inadequate. Use of a gasoline-fired preheater has been proposed but is considered to require a relatively bulky, complex and expensive heater structure. Another proposal has been to augment hot-water-based heating of the compartment by use of electrically-heated seats. Again, that approach seems to result in a complex and expensive system. It has also been proposed to add a supplemental electrical resistance heater using self-regulating heater elements of positive temperature coefficient of resistivity. Use of that type of electrical resistance heating to supplement hot-water-based heating has resulted in reductions in compartment heat-up time and has increased steady state passenger compartment temperature where desired. However, it is also found that, where today's automotive vehicles have many different electrically operated components competing for the available electrical power furnished by the vehicle power source, such supplemental electrical resistance heaters frequently cannot be large enough to provide all of the heat which may be desired, particularly during the period immediately after engine start-up on a cold day. Frequently it is found that forced circulation of air through the heating system before engine warm-up occurs can actually detract from passenger comfort by circulating air which is not heated or heated only a few degrees above a cold ambient temperature.
It would be desirable to provide a compartment heater system which can add to passenger comfort in the vehicle compartment substantially immediately after start-up on a cold day while also assuring that the passenger compartment is heated to a desired steady state temperature as rapidly as possible with the available power and while also assuring that the electrical power requirement of the system is properly matched to the available electrical power under all vehicle operating conditions.